Wireless sensor system and bearing device having wireless sensor

ABSTRACT

A wireless sensor system of the present invention includes wireless sensor units ( 4 A,  4 B) and a sensor signal receiving unit ( 5 ). The sensor units ( 4 A,  4 B) have sensors ( 6 A,  6 B), an electric power receiver ( 8 A,  8 B) for securing the electric power from an electromagnetic wave of a power feeding frequency f 1  through a tuning circuit and a detecting and rectifying circuit, and sensor signal transmitters ( 9 A,  9 B) for transmitting the signals outputted from the sensors as a wireless sensor signal of the electromagnetic wave of unique frequencies f 2  and f 3  different from the power feeding frequency f 1.  The sensor signal receiving unit ( 5 ) has an electric power transmitter ( 12 ) for transmitting the electromagnetic wave of the power feeding frequency f 1  to the units ( 4 A,  4 B) and a sensor signal receiver ( 13 ) for receiving wireless the sensor signals of the respective frequencies f 2  and f 3  transmitted from the units ( 4 A,  4 B).

FIELD OF THE INVENTION

The present invention generally relates to a wireless sensor system forwireless receiving a detection signal indicative of, for example, thetire pressure or the number of revolutions of a wheel in an automotivevehicle. The present invention also relates to a bearing assemblyequipped with such wireless sensor system and a wheel support bearingassembly equipped with such wireless sensor system.

BACKGROUND ART

It is known that various sensors are employed in automotive vehicles andvarious industrial machines to detect various target parameters such asthe number of revolutions, the temperature and the vibration of bearingassembly and/or any other movable component parts with a view tocontrolling of the machines and supervision of machine statuses. Outputsgenerated from those sensors are generally transmitted through a wiredcommunication system. However, it has often been experienced that thewired communication system is available only where wiring is possible,and where no wiring is possible, a wireless sensor system that transmitssensor signals wireless in the form of wireless electromagnetic signalsis available. In this wireless sensor system, a transmitter is generallyequipped with a compact battery.

By way of example, as far as automotive vehicles are concerned, in orderto improve the safety of automotive vehicles by means of an earlydetection of a tire puncture or prediction of blowout through detectionof the tire pressure being reduced, it is a recent trend to impose anobligation to utilize a tire pressure sensor for detecting the decreaseof the tire pressure. Most of the conventional air pressure sensors forthis purpose are generally of a design in which the detection signalindicative of the tire pressure is transmitted wireless to an automotivebody structure by means of an electromagnetic wave. The wirelesstransmitter for transmitting the detection signal wireless from the airpressure sensor to the automotive body structure is, in most cases,integrated with a compact battery built therein so that the wirelesstransmitter can be electrically powered.

On the other hand, the anti-lock brake system (ABS) for controlling anautomotive brake system by detection of the number of revolutions of thewheel with a rotation sensor has been well known. In this anti-lockbrake system, in order to avoid an automobile accident resulting frombreakage of a wiring system for the rotation sensor and also to minimizethe cost of assemblage, the detection signal, indicative of the numberof revolutions of the automobile wheel, generated by the rotation sensoris transmitted wireless in the form of an electromagnetic wave, such asdisclosed in the Japanese Laid-open Patent Publication No. 2001-151090.

The Japanese Laid-open Patent Publication No. 2002-55113, for example,discloses a rotation sensor in the form of a multipolar electric powergenerator. The multipolar electric power generator is utilized not onlyto supply an electric power both the sensor and the wirelesstransmitter, but also to detect the number of revolutions of theautomobile wheel. According to this patent publication, no supply of anelectric power from the automotive body structure to the rotation sensoris needed and, accordingly, the system as a whole can be advantageouslyassembled compact.

The sensor system utilizing the battery has the following problems.

In the first place, since the battery has a limited life, routinebattery replacement is necessary resulting in complicated and cumbersomemanagement of the lifetime of the battery. Other problems are associatedwith the environmental contamination resulting from disposal of thebattery. In addition, where the rotation sensor utilizing the battery isused in a wheel support bearing assembly or in detecting the tirepressure, an unbalanced wheel rotation may occur as a result of increaseof the sensor weight.

On the other hand, in the rotation sensor capable of generating theelectric power, the electric power is generated only when the wheelstarts its rotation. Therefore, the detection of the number ofrevolutions of the wheel tends to be unstable when the wheel rotates atan extremely low speed approximating to a halt, although the rotationsensor works satisfactorily when the wheel rotates at a speed equal toor higher than about 10 Km/h, at which the ABS is often activated. Also,this type of the rotation sensor cannot be used to detect other targetparameters such as the temperature.

As discussed above, the self-generating rotation sensor is not capableof generating or supplying an electric power in some cases.Particularly, where sensors other than a rotation-detecting sensor areutilized, it has been found difficult to secure supply of an electricpower to the sensors and transmission of sensor signals from thosesensors.

DISCLOSURE OF THE INVENTION

In view of the foregoing, the present invention has for its essentialobject to provide an improved wireless sensor system, which islight-weighted and compact in structure and can easily be serviced, andwhich can be actively used in communication at any time, while beingcapable of accomplishing both supply of an electric power to a pluralityof wireless sensors and transmission of wireless sensor signals.

Another important object of the present invention is to provide animproved wireless sensor system, which is light-weighted and compact instructure and can easily be serviced, and which can be actively used incommunication at any time, while being capable of accomplishing bothsupply of an electric power to a plurality of wireless sensor units andtransmission of wireless sensor signals.

A further object of the present invention is to provide a wirelesssensor system of an automobile vehicle, which is capable of transmittinga wireless sensor signal indicative of, for example, the tire pressureand/or the number of revolutions of the vehicle wheel, reduction in costand maintenance-free as a result of elimination of use of any battery,securement of a balanced wheel rotation resulting from reduction inweight and operation of the sensor even at an extremely low speedrotation of the wheel.

A still further object of the present invention is to provide a bearingassembly equipped with a wireless sensor unit and a wheel supportbearing assembly equipped with a wireless sensor unit, which arelight-weighted and compact in structure and can easily be serviced, andwhich can be actively used in communication at any time, while beingcapable of both supply of an electric power to a plurality of wirelesssensors and transmission of wireless sensor signals.

In order to accomplish the foregoing objects of the present invention, awireless sensor system according to a first aspect of the presentinvention includes a plurality of sensors (6A to 6E) for detectingrespective parameters to be detected, a sensor signal transmitter (9A,9B, 9) for transmitting wireless sensor signals outputted respectivelyfrom the sensors (6A to 6E), an electric power receiver (8A, 8B, 8) forreceiving wireless an electric operating power required to drive thesensors (6A to 6E) and the sensor signal transmitter (9A, 9B, 9), asensor signal receiver (13) for receiving the sensor signals transmittedfrom the sensor signal transmitter (9A, 9B, 9) and an electric powertransmitter (12) for transmitting the electric operating power wirelessto the electric power receiver (8A, 8B, 8). Wireless transmission of thesensor signals and the electric operating power may be carried out bythe utilization of not only electromagnetic waves, but also any ofmagnetic coupling, optical beams and ultrasonic waves, and any wirelesstransmission technique can be employed in the practice of the presentinvention.

According to this aspect of the present invention, since the pluralsensors (6A to 6E) and the sensor signal transmitter (9A, 9B, 9) areboth electrically powered by the electric operating power transmittedwireless from the electric power transmitter (12), neither the batterynor any electric generator as an electric power source for the sensors(6A to 6E) need be employed and, accordingly, the wireless sensor systemcan be designed compact and light-weighted and is substantiallymaintenance-free since no replacement of the battery is required. Unlikethe rotation sensor capable of self-generation, the wireless sensorsystem of the present invention is capable of performing detection andtransmission at any time regardless of operating statuses of the machineand equipment employing the wireless sensor system.

In this wireless sensor system, the sensor signal receiver (13) may havea capability of receiving the sensor signals from the respective sensors(6A to 6E), which are transmitted by the sensor signal transmitter (9A,9B, 9), and the electric power transmitter (12) may be disposed in asensor signal receiving unit (5, 5A) including the sensor signalreceiver (13). In this case, since the common sensor signal receivingunit (5, 5A) operates to receive the sensor signals from the pluralsensors (6A to 6E) and transmission of the electric operating power tothe electric power receiver (8A, 8B, 8), the wireless sensor system as awhole can be simplified in structure.

The wireless sensor system may include a plurality of wireless sensorunits (4A, 4B) each including the sensors (6A, 6B), the sensor signaltransmitter (9A, 9B) and the electric power receiver (8A, 8B). While thesensors (6A, 6B), the sensor signal transmitter (9A, 9B) and theelectric power receiver (8A, 8B) are provided separately, they may beintegrated together to provide a unitary structure that can easily behandled. By way of example, the sensors (6A, 6B), the sensor signaltransmitter (9A, 9B) and the electric power receiver (8A, 8B) areaccommodated within a common casing or provided on a common board, orthe sensor signal transmitter (9A, 9B) and the electric power receiver(8A, 8B) are integrated together to form a receiver-transmitter subunitwhile the sensors (6A, 6B) are connected to the receiver-transmittersubunit by means of an electric wiring.

In this case, since each of the plural wireless sensor units (4A, 4B)includes the sensors (6A, 6B), the sensor signal transmitter (9A, 9B)and the electric power receiver (8A, 8B) so that each sensor unit (4A,4B) can perform the transmission of the sensor signals and the receiptof the electric power, the wireless sensor units (4A, 4B) can bedisposed separated from each other, resulting in large freedom ofdisposition of the wireless sensor units (4A, 4B).

In the practice of the present invention, as shown in FIG. 8corresponding to a preferred embodiment thereof, the wireless sensorsystem may include a single wireless sensor unit (4), which in turnincludes a plurality of the sensors (6C to 6E), the sensor signaltransmitter (9) and the electric power receiver (8). The sensor signaltransmitter (9) of this single wireless sensor unit (4) transmits thesensor signals of the plural sensors (6C to 6E) wireless. In this case,since the sensor signals outputted respectively from the plural sensors(6C to 6E) can be transmitted through the single signal transmitter (9),the structure can be further simplified and become compact.

Where the plural wireless sensor units (4A, 4B) are employed, some orall of the plural wireless sensor units (4A, 4B) may include the pluralsensors (6C to 6E). In such case, each sensor signal transmitter in suchsome or all of the wireless sensor units (4A, 4B) is operable totransmit the sensor (detection) signals of the plural sensors (6C to6E). According to this feature, the wireless sensor unit (4A, 4B)including the plural sensors (6C to 6E) or the wireless sensor unit (4A,4B) including the single sensor (6A, 6B) can be chosen depending on themachine and equipment requiring the sensor unit (4A, 4B) and, therefore,the present invention can advantageously be applied in many ways.

According to a second aspect of the present invention, there is provideda wireless sensor system which includes a plurality of wireless sensorunits (4A, 4B) and a sensor signal receiving unit (5, 5A) for supplyingwireless an electric power to each of those wireless sensor units (4A,4B) and for receiving a sensor signal transmitted from each of thosewireless sensor units (4A, 4B). Each of the wireless sensor units (4A,4B) includes an electric power receiver (8A, 8B) including a tuningcircuit and a detecting and rectifying circuit for securing an electricoperating power from an electromagnetic wave of a predetermined powerfeeding frequency; a sensor (6A, 6B) for detecting a parameter to bedetected; and a sensor signal transmitter (9A, 9B) for transmitting asignal detected by the sensor (6A, 6B) as a wireless sensor signal inthe form of an electromagnetic wave of a natural frequency differentfrom the power feeding frequency. The sensor signal receiving unit (5,5A) includes an electric power transmitter (12) for transmittingwireless the electromagnetic wave of the predetermined power feedingfrequency and a sensor signal receiver (13) for receiving the wirelesssensor signal of the natural frequency that is transmitted wireless fromeach of the wireless sensor units (4A, 4B).

According to this second aspect of the present invention, since theelectric operating power can be supplied in the form of theelectromagnetic wave from the electric power transmitter (12) to each ofthe wireless sensor units (4A, 4B), neither a battery nor an electricgenerator for providing an electric operating power need be employed inthe sensor units and, therefore, not only can the sensor units (4A, 4B)be assembled compact and lightweight, but also the maintenance caneasily be accomplished because of elimination of the need to perform abattery replacement. Also, since the single sensor signal receiving unit(5, 5A) is employed to supply wireless the electric operating power toeach of the plural wireless sensor units (4A, 4B) and also to receivethe wireless sensor signal transmitted from each of the plural wirelesssensor units (4A, 4B), the wireless sensor system as a whole canadvantageously be simplified in structure.

The sensor signal receiver (13) of the sensor signal receiving unit (5)may include a plurality of receiving circuits (13 a) each operable toreceive a single frequency corresponding to the assigned naturalfrequency transmitted from each of the wireless sensor units (4A, 4B).The use of the independent and separate receiving circuits (13 a) makesit possible for each of the receiving circuits (13 a) to be simplifiedin structure.

Also, the sensor signal receiver (13) of the sensor signal receivingunit (5) may include a plurality of tuning circuits (37A, 37B) eachoperable to receive a single frequency corresponding to the assignednatural frequency transmitted from each of the wireless sensor units(4A, 4B), and a switching detector (41) for switching between outputs ofthe tuning circuits (37A, 37B) to select the outputs one at a time on atime sharing basis and for detecting each of the selected outputs.According to this structural feature, although the switching detector(41) requires the use of a switching means, the single detector (42) iseffective to discriminate and detect the wireless sensor signals and,therefore, even where the number of the wireless sensor units (4A, 4B)employed is large, the sensor signal receiving unit (5A) can besimplified in structure.

Preferably, the sensor signal receiver (13) of the sensor signalreceiving unit (5A) is capable of varying a receiving frequency and iscapable of receiving the plural wireless sensor signals by switchingamong the varying receiving frequencies on a time sharing basis. By wayof example, the sensor signal receiver (13) of the sensor signalreceiving unit (5) may include a single tuning circuit capable ofvarying a tuning frequency in correspondence with the natural frequencytransmitted from each of the wireless sensor units (4A, 4B), and acircuit for switching and detecting the natural frequency of the tuningcircuit on a time sharing basis.

In the case of this circuit construction, a means for varying a tuningfrequency is required. However, where the number of the receivingfrequencies is large, there is no need to use a plurality of tuningcircuits and, therefore, simplification of the structure and reductionof the weight of the sensor signal receiving unit (5) are possible.

In the practice of the present invention, the plane of polarization ofthe electromagnetic wave for power feeding may be different from that ofthe electromagnetic wave of the wireless sensor signal. While the use ofthe different frequencies between the electromagnetic wave for the powerfeeding and the electromagnetic wave for the wireless sensor signal iseffective to avoid any possible interference brought about by thetransmitted electric power on the receiving circuit, the use of thedifferent planes of polarization of such electromagnetic waves iseffective to enhance the signal separation between the wireless sensorunit (4A, 4B) and the sensor signal receiving unit (5A).

Also, the respective electromagnetic waves of the wireless sensorsignals transmitted from the associated wireless sensor units (4A, 4B)may have different planes of polarization. While by using the differentfrequencies for the wireless sensor signals signal reception can bediscriminated, the use of the different planes of polarization iseffective to enhance the signal separation between the wireless sensorunits (4A, 4B).

In the practice of the present invention, as shown in FIG. 7 where theplural wireless sensor units (4A, 4B) are employed, those wirelesssensor units (4A, 4B) may be mounted on different bearings (51, 52) in amachine plant (53). The machine plant (53) may include a machineinstalled in a factory such as an industrial machine, a machine tooland/or a transport machine, or a railway car and/or an automotivevehicle. The bearings (51, 52) may be a rolling bearing or the like. Byway of example, the machine plant (53) may a conveyor line and each ofthe bearings (51, 51) on which the wireless sensor unit (4A, 4B) ismounted may be a bearing for supporting a drive roller of the conveyor.

Also, where the plural wireless sensor units (4A, 4B) are employed, asshown in FIG. 4 or FIG. 6, at least one of the plural wireless sensorunits (4A, 4B) may include the sensor (6A) utilized as a tire pressuresensor for detecting a tire pressure of an automotive vehicle or arotation sensor for a wheel support bearing assembly. Alternatively,each of the wireless sensor units (4A, 4B) may include both a tirepressure sensor (6B) and a rotation sensor (6A). The rotation sensor(6A) acts as a wheel rotation sensor.

Where the wireless sensor unit (4A, 4B) includes a tire pressure sensoras the sensor (6B), no battery is necessary in the present inventionand, therefore, not only is the maintenance-free possible with respectto the battery replacement, but a balance of a wheel can also be securedas a result of reduction in weight. On the other hand, where thewireless sensor unit (4A, 4B) includes a wheel rotation sensor as thesensor (6A), unlike an electric power generator generating an electricpower in response to rotation of the vehicle wheel, the electric powercan be supplied from the electric power transmitter (12) mounted on thevehicle body structure even when the automotive vehicle is halted and,therefore, the use of the sensor (6A) in combination with an activesensor such as a Hall IC (integrated circuit) makes it possible toachieve a generally so-called zero velocity detection (i.e., detectionof the rotation in a condition in which the automotive vehicle issubstantially halted). Accordingly, the running stability can beobtained by means of a highly sophisticated control such as a control ofthe ABS activation shortly before the automotive vehicle then running ona low frictional road surface is brought to a halt, and a tractioncontrol at the time of abrupt acceleration and at the time of anextremely low speed run.

Where the wireless sensor unit (4B) for the tire pressure and thewireless sensor unit (4A) for the detection of the wheel rotation areboth employed, since those wireless sensor units (4A, 4B) are disposedin the vicinity of a wheel within the same tire house, not only can thesupply of the electric power to the plural wireless sensor units (4A,4B) easily be accomplished, but also transmission of the wireless sensorsignals can be achieved by a feeble magnetic wave.

According to a third aspect of the present invention, the presentinvention also provides a bearing assembly equipped with a wirelesssensor unit, which includes a plurality of wireless sensor units (4A,4B) mounted on a bearing. Each of the wireless sensor units (4A, 4B)includes a sensor (6A, 6B) for detecting a parameter to be detected, asensor signal transmitter (9A, 9B) for transmitting wireless a sensorsignal outputted from the sensor (6A, 6B), and an electric powerreceiver (8A, 8B) for receiving wireless an electric operating powerrequired to drive the sensor (6A, 6B) and the sensor signal transmitter(9A, 9B).

According to the third aspect of the present invention, while the supplyof the electric power to the plural sensors (6A, 6B) and thetransmission of the sensor signals from the plural sensors (6A, 6B) canbe accomplished, not only can the bearing assembly of a lightweight andcompact structure be achieved, but the maintenance is also easy, andeven when the bearing assembly is in a halted condition, thecommunication is possible.

According to a fourth aspect of the present invention, there is provideda bearing assembly (33) equipped with a wireless sensor unit, whichincludes one of a plurality of wireless sensor units (4A, 4B) that ismounted on a bearing. Each of the plural wireless sensor units (4A, 4B)includes a sensor (6A, 6B) for detecting a parameter to be detected; asensor signal transmitter (9A, 9B) for transmitting wireless a sensorsignal outputted from the sensor (6A, 6B), and an electric powerreceiver (8A, 8B) for receiving wireless an electric operating powerrequired to drive the sensor (6A, 6B) and the sensor signal transmitter(9A, 9B). The plural wireless sensor units (4A, 4B) are operable totransmit to a common sensor signal receiver (13) the respective sensorsignals transmitted from the corresponding sensor signal transmitters(6A, 6B) and is also operable to receive the electric operating powerwireless from a common electric power transmitter (12) through theelectric power receiver (8A, 8B).

According to the third aspect of the present invention, the wirelesssensor unit (4A, 4B), mounted on the bearing, and the wireless sensorunit (4A, 4B) mounted on any other machine or equipment can transmit thesensor signals to the common sensor signal receiver (13) and can beelectrically powered by the electric power transmitter (12) and,accordingly, the bearing assembly of a simplified structure can beprovided.

The present invention in accordance with a fifth aspect thereof providesa bearing assembly equipped with a wireless sensor, which includes aplurality of sensors (6C to 6E) for detecting respective parameters tobe detected, a sensor signal transmitter (9) for transmitting wirelesssensor signals outputted from the respective sensors (6C to 6E), and anelectric power receiver (8) for receiving wireless an electric operatingpower required to drive the sensors (6C to 6E) and the sensor signaltransmitter (9).

According to the fifth aspect of the present invention, the pluralsensors (6C to 6E), for example, the rotation sensor, the temperaturesensor and the vibration sensor can be mounted on a bearing and thesensor signals outputted therefrom can be transmitted through the sensorsignal transmitter (9). Receipt of the electric power can also beperformed through the common electric power receiver (8) and, therefore,the bearing assembly of a simplified structure can be provided.

In the bearing assembly equipped with the wireless sensor of any of theforegoing structures in accordance with the present invention, at leastone of the sensors (6 a to 6E) mounted on the bearing may be a rotationsensor which includes a multipolar magnet (17), having a plurality ofmagnetic poles deployed in a direction circumferentially thereof, and amagnetic sensor (18) for detecting the magnetic poles of the multipolarmagnet. The magnetic sensor (18) is preferably in the form of amagnetoresistive sensor.

Where the rotation sensor is made up of the multipolar magnet (17) andthe magnetic sensor (18), it is possible to construct a compact rotationsensor having a high resolution. Also, the magnetoresistive sensor (18)consumes a relatively small amount of electric power and, therefore, canbe suitably utilized in combination with the wireless electric powerfeeding that is generally low in efficiency of electric power feeding ascompared with the wired system.

In the bearing assembly equipped with the wireless sensor of any of theforegoing structures in accordance with the present invention, thesensor (6A to 6E) may be preferably disposed within a sealed space inthe bearing assembly, which is shielded from the outside, and theelectric power receiver (8, 8A, 8B) and the sensor signal transmitter(9, 9A, 9B) may then be disposed outside the bearing. The sealed spaceis, for example, an annular bearing space defined between an outer raceand an inner race of a rolling bearing and sealed at opposite open endsby sealing members. Where the bearing is a wheel support bearing, thesealed bearing space is defined between an inner member (2) and an outermember (1).

Where the sensors (6A to 6E) are accommodated within the sealed space ofthe bearing assembly, the sensors (6A to 6E) can advantageously beprotected from external dusts, foreign matter, water and so on and,therefore, the reliability and durability of the sensors (6A to 6E) canincrease. In particular, where the bearing assembly is a wheel supportbearing assembly (33), the bearing assembly is often placed under thesevere environment where it is susceptible to foreign matter and/orsalty muddy water on the roadway and, therefore, disposition of thesensors (6C to 6E) within the sealed space is effective to increase thereliability and durability thereof. The electric power receiver (8, 8A,8B) and the sensor signal transmitter (9, 9A, 9B) are preferablydisposed outside the bearing assembly in terms of wireless transmissionefficiency.

According to a sixth aspect of the present invention, there is provideda wheel support bearing assembly (33) for rotatably supporting a vehiclewheel relative to a vehicle body structure, which includes an outermember (1) having a plurality of outer raceways, an inner member (2)having inner raceways aligned with the outer raceways, and a pluralityof rows of rolling elements (3) interposed between the outer racewaysand the inner raceways. This wheel support bearing assembly (33) alsoincludes one of a plurality of wireless sensor units (4A, 4B) that ismounted on the wheel support bearing assembly (33). Each of the pluralwireless sensor units (4A, 4B) includes a sensor (6A, 6B) for detectinga parameter to be detected, a sensor signal transmitter (9A, 9B) fortransmitting wireless a sensor signal outputted from the sensor (6A,6B), and an electric power receiver (8A, 8B) for receiving wireless anelectric operating power required to drive the sensor (6A, 6B) and thesensor signal transmitter (9A, 9B). Also, those plural wireless sensorunits (4A, 4B) operate to transmit the respective sensor signals to acommon sensor signal receiver (13) through the corresponding sensorsignal transmitters (9A, 9B) and also operate to receive the electricoperating power wireless from a common electric power transmitter (12)through the electric power receiver (8A, 8B).

According to the sixth aspect of the present invention, while the supplyof the electric power to the plural wireless sensor units (4A, 4B) andthe transmission of the sensor signals from the plural wireless sensorunits (4A, 4B) can be accomplished, not only can the wheel supportbearing assembly (33) of a lightweight and compact structure beachieved, but the maintenance is also easy, and even when the bearingassembly is in a halted condition, the communication is possible.

The present invention in accordance with a seventh aspect thereofprovides a wheel support bearing assembly (33) for rotatably supportinga vehicle wheel relative to a vehicle body structure, which includes anouter member (1) having a plurality of outer raceways, an inner member(2) having inner raceways aligned with the outer raceways, and aplurality of rows of rolling elements (3) interposed between the outerraceways and the inner raceways. In this wheel support bearing assembly(33), there are provided a plurality of sensors (6C to 6E) for detectingrespective parameters to be detected, a sensor signal transmitter (9)for transmitting wireless sensor signals outputted from the respectivesensors (6C to 6E), and an electric power receiver (8) for receivingwireless an electric operating power required to drive the sensors (6Cto 6E) and the sensor signal transmitter (9).

According to the seventh aspect of the present invention, while thesupply of the electric power to the plural sensors (6C to 6E) and thetransmission of the sensor signals from the plural sensors (6C to 6E)can be accomplished, not only can the bearing assembly (33) of alightweight and compact structure be achieved, but the maintenance isalso easy, and even when the bearing assembly is in a halted condition,the communication is possible. Also, mounting of the plural sensors (6Cto 6E) on the bearing allows not only the number of revolutions but alsoother parameters such as temperature, vibration, load, torque and/orpressure to be detected and, therefore, is effective to render thebearing assembly to be intelligent, thus upgrading the automobilecontrol. In addition, based on bearing information such as temperature,the bearing assembly can be diagnosed to determine if it has anytrouble. It is, however, to be noted that, similar effects brought aboutby the use of the plural sensors (6C to 6E) can be obtained even whenthe plural sensors (6C to 6E) are mounted on any bearing assemblies ingeneral other than the wheel support bearing assembly discussed above.

In the wireless sensor system of the present invention, where one of thesensors (6A to 6E) is mounted on a wheel support bearing assembly, forexample, where the wireless sensor system includes any of the wheelsupport bearing assemblies (33), a sensor signal receiver (13) forreceiving a sensor signal transmitted from the sensor signal transmitter(9, 9A, 9B) in the wheel support bearing assembly (33), and an electricpower transmitter (12) for transmitting wireless the electric operatingpower to the electric power receiver (8, 8A, 8B), the sensor signalreceiver (13) and the electric power transmitter (12) may be disposed ina tire house (34 a) of the vehicle body structure (34), where the wheelsupport bearing assembly (33) is installed, or may be disposed in aportion of the vehicle body structure (34), which is more distant fromthe tire house (34 a) with respect to the wheel support bearing assembly(33). That portion more distant from the tire house (34 a) with respectto the wheel support bearing assembly (33) is, for example, a dashboardor console, where instruments (EUC or the like) utilized to perform anelectric control of the automotive vehicle are installed.

According to this aspect of the present invention, disposition of thesensor signal receiver (13) and the electric power transmitter (12) atthat portion more distant from the tire house (34 a) with respect to thewheel support bearing assembly (33) is effective to eliminate the use ofany harness which would otherwise be required between the tire house (34a) and the wheel support bearing assembly (33) and, accordingly, notonly can troubles such as breakage of the harness resulting fromcollision of stone be avoided, but also the wireless sensor system canbe light-weighted. Also, where the sensor signal receiver (13) and theelectric power transmitter (12) are disposed in the tire house (34 a),the distance in which the wireless transmission is carried out can beset short and, therefore, the intensity of the electromagnetic waves canadvantageously be reduced, resulting in minimized electric powerconsumption.

The wireless sensor system of the present invention according to oneaspect thereof includes the plural sensors for detecting the respectiveparameters to be detected, the sensor signal transmitter fortransmitting wireless the sensor signals outputted respectively from thesensors, the electric power receiver for receiving wireless the electricoperating power required to drive the sensors and the sensor signaltransmitter, the sensor signal receiver for receiving the sensor signalstransmitted by the sensor signal transmitter, and the electric powertransmitter for transmitting wireless the electric operating power tothe electric power receiver. Accordingly, this wireless sensor systemcan be designed as a system, which is, while the supply of the electricpower to the plural sensors and the transmission of the sensor signalsfrom the plural sensors can be accomplished, a lightweight and compactstructure. Also, the maintenance of the wireless senor system is easyand even when the bearing assembly is in a halted condition, thecommunication is possible at any time.

The wireless sensor system of the present invention according to anotheraspect thereof is so designed that the electric operating power can besupplied wireless by the common sensor signal receiving unit to theplural wireless sensor units and, accordingly, the supply of theelectric operating power to the plural wireless sensor units and thetransmission of the sensor signals can be accomplished with a simplifiedstructure. In view of this, not only is the maintenance such asreplacement of the battery eliminated substantially, but also thereduction of the weight and the possibility of the sensor operation,which does not depend on the operating statuses of the machine andequipments, in which the wireless sensor system of the present inventionis installed, can be appreciated. Since the wireless sensor system isreduced in weight, the unbalance can advantageously be minimizedparticularly where the wireless sensor unit is fitted to a rotatingelement of the bearing.

Where the wireless sensor unit is used in association with a tirepressure sensor for detecting the tire pressure in an automotivevehicle, the use of any battery or a similar external power source canadvantageously be eliminated, resulting in reduction of the cost,maintenance-free and increase of the wheel balance brought about by thereduction of the weight. Also, where the wireless sensor unit is used inassociation with the rotation sensor mounted on a wheel support bearingassembly for an automotive vehicle, the electric power can be suppliedeven during a halted condition of the vehicle wheel and, therefore, thenumber of revolutions can be detected even though the vehicle wheel isalmost halted, enabling the running stability to be obtained by means ofa highly sophisticated control such as a control of the ABS activationshortly before the automotive vehicle then running on a low frictionalroad surface is brought to a halt, and a traction control at the time ofabrupt acceleration and at the time of an extremely low speed run.

With the bearing assembly equipped with the wireless sensor and thewheel support bearing assembly equipped with the wireless sensor, bothdeveloped in accordance with the present invention, advantages can beappreciated in that the bearing assembly is lightweight and compact instructure and, yet, substantially free of maintenance, in that even whenthe bearing assembly is in a halted condition, the communication ispossible at any time while the supply of the electric power to theplural sensors and the transmission of the sensor signals from theplural sensors take place.

BRIEF DESCRIPTION OF THE DRAWINGS

In any event, the present invention will become more clearly understoodfrom the following description of preferred embodiments thereof, whentaken in conjunction with the accompanying drawings. However, theembodiments and the drawings are given only for the purpose ofillustration and explanation, and are not to be taken as limiting thescope of the present invention in any way whatsoever, which scope is tobe determined by the appended claims. In the accompanying drawings, likereference numerals are used to denote like parts throughout the severalviews, and:

FIG. 1 is a block diagram showing a wireless sensor system according toa first embodiment of the present invention;

FIG. 2 is a circuit block diagram showing the wireless sensor systemshown in FIG. 1;

FIG. 3 is a circuit block diagram of a sensor signal receiving unitemployed in the wireless sensor system according to a second preferredembodiment of the present invention;

FIG. 4 is a schematic longitudinal sectional view of a wheel supportbearing assembly equipped with the wireless sensor system according toany one of the first and second preferred embodiments of the presentinvention;

FIG. 5 is a longitudinal sectional view showing a portion of anautomobile wheel in which a wireless sensor unit of the wireless sensorsystem according to any one of the first and second preferredembodiments of the present invention is incorporated for transmitting asensor signal indicative of the tire pressure;

FIG. 6 is a schematic longitudinal sectional view of the wheel supportbearing assembly equipped with the wireless sensor system, showing amodification thereof;

FIG. 7 is a schematic sectional diagram showing an equipment equippedwith the wireless sensor system according to a third preferredembodiment of the present invention;

FIG. 8 is a block diagram showing the wireless sensor system accordingto a fourth preferred embodiment of the present invention;

FIG. 9 is a block diagram of the wireless sensor system shown in FIG. 8,shown together with the wheel support bearing assembly to which it isapplied; and

FIG. 10 is a longitudinal sectional view showing the details of thewheel support bearing assembly of FIG. 9.

BEST MODE FOR CARRYING OUT THE INVENTION

A first preferred embodiment of the present invention will now bedescribed with particular reference to FIG. 1. As shown therein, awireless sensor system of the present invention includes a plurality of,for example, two, wireless sensor units 4A and 4B and a common sensorsignal receiving unit 5 for supplying an electric power wireless to eachof the wireless sensor units 4A and 4B and also for receiving a sensorsignal transmitted from each of those wireless sensor units 4A and 4B.It is to be noted that the number of the wireless sensor units that canbe employed in the practice of the present invention is not particularlylimited to two as shown.

Each of the sensor units 4A and 4B includes a sensor 6A or 6B, whichserves as a means for detecting a target parameter to be detected, and areceiver-transmitter subunit 7A or 7B, which in turn includes anelectric power receiver 8A or 8B and a sensor signal transmitter 9A or9B.

As shown in FIG. 2, each of the electric power receivers 8A and 8Bdefines a means including a tuning circuit 10A or 10B and a detectingand rectifying circuit 11A or 11B for processing an electromagnetic waveof a predetermined power feeding frequency f1 to provide an electricoperating power. The electric operating powers from the respectiveelectric power receivers 8A and 8B are utilized to electrically drivethe sensors 6A and 6B and the sensor signal transmitters 9A and 9B,respectively. Each of the electric power receivers 8A and 8B isconstructed of the tuning circuit 10A or 10B including an antenna 22 andan LC circuit 23, and the detecting and rectifying circuit 11A or 11Bincluding a diode 24 and a capacitor 25.

Each of the sensor signal transmitters 9A and 9B defines a means fortransmitting a signal, outputted from the sensor 6A or 6B, in the formof an electromagnetic wireless sensor signal of a natural frequency f2or f3 different from the power feeding frequency f1 and includes anantenna 19, an LC circuit 20 and a semiconductor switching element 21.

The common sensor signal receiving unit 5 includes an electric powertransmitter 12 for transmitting the electromagnetic wave of thepredetermined power feeding frequency f1, and a sensor signal receiver13 for receiving the wireless sensor signals of the natural frequenciesf2 and f3 that are transmitted respectively from the wireless sensorunits 4A and 4B. The electric power transmitter 12 includes a highfrequency generator 26 and a transmitting circuit 27. The transmittingcircuit 27 includes an antenna 28, an LC circuit 29 and a semiconductorswitching element 30.

The sensor signal receiver 13 of the common sensor signal receiving unit5 includes receiving circuits 13 a equal in number to and operativelyassociated with the respective wireless sensor units 4A and 4B. Each ofthe receiving circuits 13 a of the sensor signal receiver 13 is acircuit for receiving a signal of a single frequency corresponding tothe natural frequency f2 or f3 that is transmitted from the wirelesssensor units 4A or 4B, and includes a tuning circuit 37 and a detectingcircuit 38. The tuning circuit 37 in turn includes an antenna 30 and anLC circuit 40.

The plane of polarization of the power feeding electromagnetic wave thatis transmitted from the sensor signal receiving unit 5 differs from thatof the electromagnetic waves of the sensor signals transmitted from therespective wireless sensor units 4A and 4B. The use of the differentplanes of polarization in addition to the use of the differentfrequencies is effective to avoid any possible interference of the powerfeeding electromagnetic wave with the electromagnetic waves of thesensor signals to thereby enhance the signal separation. Also, therespective electromagnetic waves of the sensor signals transmitted fromthe wireless sensor units 4A and 4B have respective planes ofpolarization that are different from each other, so that any possibleinterference between the electromagnetic waves of the sensor signals canbe avoided to enhance the signal separation.

With the wireless sensor system so constructed as hereinabove described,an electric operating power required for each of the wireless sensorunits 4A and 4B can be supplied wireless and, accordingly, neither thebattery nor an electric power generator for providing an electric powernecessary to feed the sensor units 4A and 4B is required, resulting inthe wireless sensor system to be assembled compact and lightweight. Inaddition, no routine battery replacement is required and, hence, themaintenance of the wireless sensor system can be facilitated. Yet, sinceboth the wireless supply of the electric power to each of the wirelesssensor units 4A and 4B and receipt of the wireless sensor signal fromeach of the wireless sensor units 4A and 4B are accomplished with thecommon sensor signal receiving unit 5, the wireless sensor system as awhole can advantageously be simplified in structure.

FIG. 3 illustrates the wireless sensor system according to a secondpreferred embodiment of the present invention, in which a differentsensor signal receiving unit 5A is employed in place of the sensorsignal receiving unit 5 discussed above. In the practice of this secondpreferred embodiment of the present invention, the sensor signalreceiving unit 5A cooperates with one or more wireless sensor unitswhich are identical to the wireless sensor units 4A and 4B shown in FIG.1.

Referring now to FIG. 2, the sensor signal receiving unit 5A includes asensor signal receiver 13A made up of tuning circuits 37A and 37B, eachcapable of receiving a signal of a single frequency corresponding to thenatural frequency f2 or f3 transmitted from the corresponding wirelesssensor units 4A or 4B (FIG. 2), and a common switching detector 41 forswitching between outputs of the tuning circuits 37A and 37B to selectthe outputs one at a time on a time sharing basis and for detecting eachof the selected outputs. The switching detector 41 includes a detectingelement (detector) 42 and a switching element (selector) 43 forswitching the tuning circuits 37A and 37B, one at a time on a timesharing basis, to connect them to the detecting element 42.

Other structural features of the wireless sensor receiving unit 5Aemployed in the wireless sensor system according to the secondembodiment of the present invention are similar to the wireless sensorreceiving unit 5 employed in the wireless sensor system according to thefirst embodiment and, therefore, the details thereof are not reiteratedfor the sake of brevity.

In this second embodiment, when the switching element 43 of theswitching detector 41 connects the tuning circuit 37A to the detectingelement 42, the detecting element 42 detects a signal of the frequencyf2 which is fed wireless to the tuning circuit 37A from the wirelesssensor unit 4A for detecting the number of revolutions. On the otherhand, when the switching element 43 connects the tuning circuit 37B tothe detecting element 42, the detecting element 42 detects a signal ofthe frequency f3 which is fed wireless to the tuning circuit 37B fromthe wireless sensor unit 4B for detecting the number of revolutions.

According to the second embodiment shown in and described with referenceto FIG. 3, the respective electromagnetic waves of the naturalfrequencies f2 and f3 transmitted wireless from the associated wirelesssensor units 4A and 4B can be discriminately detected by the singledetecting element 42 in the sensor signal receiving unit 5A, the sensorsignal receiving unit 5A can have a simplified structure even where thenumber of the wireless sensor units used is large.

It is to be noted that in the second embodiment of the present inventiona single variable tuning circuit capable of varying to tune to each ofthe natural frequencies f2 and f3 transmitted respectively from thewireless sensor units 4A and 4B (FIG. 2) may be employed in place of theplural tuning circuits 37A and 37B. In such case, the sensor signalreceiver 13A should be so configured that the switching element canswitch among varying natural frequencies of the tuning circuit to selectthe varying natural frequencies one at a time on a time sharing basis,and that the detecting element 42 can then detect each of the selectednatural frequencies.

An application of the wireless sensor system according to the presentinvention to an automotive vehicle will now be described with particularreference to FIGS. 4 and 5. In this application, the wireless sensorsystem is utilized for detecting the tire pressure and the number ofrevolutions of the vehicle wheel. As shown in FIG. 4, the wheel 31 shownby the phantom line is rotatably supported by a vehicle body structure34 by means of a wheel support bearing assembly 33. The wheel supportbearing assembly 33 includes an outer member 1 supporting the wheel 31and an rotatable inner member 2, with circumferentially extending rowsof rolling elements 3 interposed between the outer member 1 and theinner member 2.

The outer member 1 is supported by a wheel suspension, extendingdownwardly from the vehicle body structure 34, through a knuckle (notshown). On the other hand, the inner member 2 is made up of a hub axle2A, which has one end formed integrally with a wheel mounting flange 2 aextending radially outwardly therefrom, and an outer race 15 a forming apart of a constant velocity universal joint 15, with the vehicle wheel31 fitted to the wheel mounting flange 2 a of the hub axle 2A. Thisinner member 2 is coupled with an axle 16 through the constant velocityuniversal joint 15.

An annular bearing space delimited between the outer member 1 and theinner member 2 has one of its opposite annular open ends provided withthe wireless sensor unit 4A for detecting the number of revolutions ofthe vehicle wheel 31. On the other hand, the wireless sensor unit 4B iscarried by the vehicle wheel 31 to detect the tire pressure. The sensorsignal receiving unit 5 for supplying wireless the electric power to thewireless sensor units 4A and 4B and for receiving respective sensorsignals transmitted wireless from the wireless sensor units 4A and 4B isfixedly secured to a portion of the vehicle body structure 34, forexample, to a tire house 34 a. It is to be noted that the sensor signalreceiving unit 5 is of the structure shown in and described withreference to any one of FIGS. 1 and 2.

The sensor 6A of FIG. 4 used as a rotation sensor includes a magneticencoder 17 mounted on the inner member 2 and a magnetic sensor 18mounted on the outer member 1 in fact-to-face relation with the magneticencoder 17. The magnetic encoder 17 is a ring-shaped multipolar magnet,which is a ferrite magnet, a rare earth rubber magnet, a plastic magnetor a sintered magnet and has opposite magnetic poles N and S alternatingin a direction circumferentially thereof. The magnetic sensor 18 is amagnetoresistive sensor, that is, a sensor utilizing a magnetoresistiveelement (also referred to as “MR element”) and is operable to detectchange in polarity of the magnetic encoder 17 as the vehicle wheel 31rotates and then to output an incremental pulse signal as a sensorsignal indicative of the number of revolutions of the vehicle wheel 31.

It is to be noted that the magnetic sensor 18 may not be always limitedto the magnetoresistive sensor, but a Hall effect sensor, an M1 sensoror a flux-gate magnetic sensor may be equally employed therefor.

When the rotation sensor is made up of the multipolar magnet and themagnetic sensor, it is possible to provide a compact rotation sensorhaving a high resolution. Also, if the magnetic sensor of themagnetoresistive type has a sensor element having a high resistance, theelectric power consumption can be minimized and, therefore, it ispreferable to combine such magnetic sensor with a wireless power feedingsystem having a low power feeding efficiency as compared with that ofthe wired system.

The wireless sensor unit 4B of FIGS. 4 and 5 for detecting the tirepressure is secured to a portion of a tire wheel 35 that confronts theinterior of a wheel tire 36 mounted on the vehicle wheel. The sensor 6Bof this wireless sensor unit 4B serves to detect the tire pressure ofthe wheel tire 36.

The operation of the wireless sensor system will now be described. Thepower feeding electromagnetic wave that is transmitted from the electricpower transmitter 12 (FIG. 1) of the sensor signal receiving unit 5mounted on the vehicle body structure 34 is received and rectified bythe electric power receivers 8A and 8B of the wireless sensor units 4Aand 4B, respectively, to provide an electric operating power with whichthe wireless sensor units 4A and 4B can be electrically powered.

The sensor 6A of the wireless sensor unit 4A mounted on the wheelsupport bearing assembly 33 detects the number of revolutions of thevehicle wheel 31. More specifically, change in polarity of the magneticencoder 17 on the inner member 2 incident to rotation of the vehiclewheel 31 is detected by the magnetic sensor 18, from which the sensorsignal is subsequently outputted in the form of the incremental pulsesignal. This sensor signal indicative of the number of revolutions ofthe vehicle wheel 31 is transmitted wireless from the sensor signaltransmitter 9A by means of the electromagnetic wave of the frequency f2as a carrier wave. One of the receiving circuits 13 a of the sensorsignal receiver 13 of the sensor signal receiving unit 5, which isoperatively associated with the wireless sensor unit 4A, receives anddetects this electromagnetic wave transmitted from the sensor signaltransmitter 9A and then outputs the sensor signal indicative of thenumber of revolutions of the vehicle wheel 31.

On the other hand, the sensor 6B of the wireless sensor unit 4B carriedby the vehicle wheel 31 detects the tire pressure of the wheel tire 36.The sensor signal indicative of the tire pressure is transmittedwireless from the sensor signal transmitter 9B by means of theelectromagnetic wave of the frequency f3 as a carrier wave. The other ofthe receiving circuits 13 a of the sensor signal receiver 13 of thesensor signal receiving unit 5, which is operatively associated with thewireless sensor unit 4B, receives and detects this electromagnetic wavetransmitted from the sensor signal transmitter 9B and then outputs thesensor signal indicative of the tire pressure.

As hereinabove described, with the wireless sensor system of the presentinvention, not only can the electric power be supplied wireless in theform of the electromagnetic wave from the sensor signal receiving unit5, mounted on the vehicle body structure 34, to each of the wirelesssensor units 4A and 4B, but the sensor signal receiving unit 5 can alsoreceive the different sensor signal transmitted wireless in the form ofthe electromagnetic wave from each of the wireless sensor units 4A and4B. Accordingly, the wireless sensor system of the present invention issubstantially free from the problem associated with battery shutoff thatis inevitable in the conventional sensor system where a battery is usedas a source of an electric power. Also, detection results such as thetire pressure and the number of revolution of the vehicle wheel can beassuredly transmitted in the form of a wireless signal and therespective sensors 6A and 6B in the wireless sensor units 4A and 4B canbe assembled compact and inexpensive. Elimination of the batteryreplacement accomplished by the present invention makes it easy to carryout the maintenance of the wireless sensor system.

Since the wireless sensor unit 4A for the detection of the number ofrevolutions, in which the magnetic sensor 18 forms a part of the sensor6A, is not of a self-generating type, that is, a type capable ofgenerating the electric operating power as the vehicle wheel 31 rotates,detection of the number of revolutions is possible even when the vehiclewheel rotates at a speed approximating to a halt, and the runningstability can be obtained by means of a highly sophisticated controlsuch as a control of the ABS activation shortly before the automotivevehicle then running on a low frictional road surface is brought to ahalt, and a traction control at the time of abrupt acceleration and atthe time of an extremely low speed run.

Also, since the wireless sensor unit 4B for the detection of the tirepressure does not require the use of any battery, the weight of the unit4B can advantageously be reduced correspondingly, allowing the wheelbalance to be secured.

It is to be noted that although the wheel support bearing assembly 33shown in FIG. 4 is of a fourth generation type, the present inventioncan be equally applied to the wheel support bearing assembly of anygeneration type, for example, the wheel support bearing assembly of athird generation type such as shown in FIG. 6. In the modification shownin FIG. 6, the inner member 2 is comprised of a hub axle 2A and an innerrace 2B fixedly mounted externally on one end of the hub axle 2A, andinner raceways are defined on respective outer peripheral surfaces ofthe hub axle 2A and the inner race 2B, respectively. Outer racewaysaligned with the respective inner raceways are defined on an innerperipheral surface of the outer member 1. The hub axle 2A is coupledwith an axle fitted into an outer race 15 a of the constant velocityuniversal joint 15 and the inner member 2 is then coupled with the outerrace 1 5 a of the constant velocity universal joint 15.

The sensor (the rotation sensor) 6A of the wireless sensor unit 4A ismade up of the magnetic encoder 17 mounted on the inner member 2 and themagnetic sensor 18 mounted on the outer member 1 in face-to-facerelation with the magnetic encoder 17. The magnetic encoder 17 ismounted on a slinger, which forms a part of a sealing device mounted onthe inner member 2. Other structural features of the wheel supportbearing assembly shown in FIG. 6 than those described above are similarto those shown in and described in connection with the previousembodiment with reference to FIGS. 4 and 5.

It is to be noted that in the wheel support bearing assembly 33 shown inany one of FIGS. 4 and 6, the wireless sensor units 4A and 4B may bearranged on the outer member 1 of the wheel support bearing assembly 33as shown by the dotted line in FIG. 6. In such case, one of the wirelesssensor units, for example, the wireless sensor unit 4A may make use ofthe rotational sensor as the sensor 6A and the other of the wirelesssensor units, that is, the wireless sensor unit 4B may make use of atemperature sensor or a vibration sensor as the sensor 6B.

FIG. 7 illustrates a third preferred embodiment of the presentinvention. In this embodiment, the present invention is applied to amachine plant 53 including a plurality of, for example, two rollingbearings 51 and 52. The bearings 51 and 52 are provided with therespective wireless sensor units 4A and 4B of FIGS. 1 and 2. The machineplant 53 may be, for example, a conveyor line including roller conveyorsor belt conveyors, in which rotary shafts 59 for driving transportrollers or belt drive rollers are rotatably supported by the rollingbearings 51 and 52, respectively.

Each of the rolling bearings 51 and 52 includes an inner race 54, anouter race 55, a row of rolling elements 56 retained by a rollerretainer 57 and rollingly interposed between the inner and outer races54 and 55, and a sealing member 58. The bearings 51 and 52 are a deepgroove ball bearing.

The wireless sensor unit 4A mounted on the rolling bearing 51 is usedfor detecting the number of revolutions and the sensor 6A of thewireless sensor unit 4A includes the magnetic encoder 17 mounted on theinner race 54 and the magnetic sensor 18 mounted on the outer race 55 inface-to-face relation with the magnetic encoder 17. On the other hand,the wireless sensor unit 4B mounted on the rolling bearing 52 includesthe sensor 6B used to detect a parameter such as the temperature or thevibration.

The sensor signal receiving unit 5 is installed at a suitable placewithin the machine plant 53, where the sensor signal receiving unit 5receives the sensor signals from the wireless sensor units 4A and 4B andtransmits the electric operating power to the wireless sensor units 4Aand 4B. Unless otherwise specified, this third embodiment issubstantially similar in structure to the embodiment shown in anddescribed with reference to FIGS. 1 and 2.

According to the third embodiment, the respective sensor signalsoutputted from the wireless sensor units 4A and 4B, which are mounted onthe associated rolling bearings 51 and 52 within the machine plant 53,are received by the common sensor signal receiving unit 5 and,concurrently, the electric operating power required to drive thewireless sensor units 4A and 4B can be supplied wireless from the commonsensor signal receiving unit 5 to the wireless sensor units 4A and 4B.

It is to be noted that although in the embodiment shown in FIG. 7reference has been made to the use of the two wireless sensor units 4Aand 4B, the machine plant 53 may include three or more rolling bearingseach incorporated with the respective wireless sensor unit so that thewireless sensor units can interface with the common sensor signalreceiving unit 5 in a manner similar to that described hereinabove.

FIG. 8 illustrates the wireless sensory system according to a fourthpreferred embodiment of the present invention. The wireless sensorsystem of FIG. 8 includes a single wireless sensor unit 4 having aplurality of, for example, three sensors 6C to 6E incorporated therein.Specifically, the wireless sensor unit 4 includes the plural sensors 6Cto 6E, a sensor signal transmitter 9 and an electric power receiver 8.

The sensor signal transmitter 9 transmits wireless respective sensorsignals from the sensors 6C to 6E to the common sensor signal receivingunit 5. The respective outputs of the sensors 6C to 6E are processed bya signal coordinator 60 so that they can be transmitted to the commonsensor signal receiving unit 5 by the sensor signal transmitter 9. Thesignal coordinator 60 may be of any suitable circuit so designed thatthe sensor signals from the sensors 6C to 6E can be processed so as tobe discriminately received by the common sensor signal receiving unit 5,and may, for example, be so designed that the sensor signals from thesensors 6C to 6E can be supplied to the sensor signal transmitter 9 on atime-shared basis. Alternatively, the signal coordinator 60 may be of atype capable of superimposing the respective sensor signals from thesensors 6C to 6E.

The electric power receiver 8 in the wireless sensor unit 4 supplies anelectric power, received wireless from the common sensor signalreceiving unit 5, to the sensors 6C to 6E, the sensor signal transmitter9 and the signal coordinator 60. The sensor signal transmitter 9, theelectric power receiver 8 and the signal coordinator 60 altogetherconstitute a receiver-transmitter subunit 7. It is to be noted that thesignal coordinator 60 may be either incorporated in the sensor signaltransmitter 9 or separate from the sensor signal transmitter 9.

The sensor signal receiving unit 5 includes a sensor signal receiver 13for receiving the sensor signal transmitted from the sensor signaltransmitter 9 of the wireless sensor unit 4, and an electric powertransmitter 12 for transmitting an electric power wireless to theelectric power receiver 8 of the wireless sensor unit 4. The sensorsignal receiver 13 is capable of discriminately receiving the respectivesensor signals, outputted from the sensors 6C to 6E and transmittedthrough the sensor signal transmitter 9, in dependence on a processingscheme of the signal coordinator 60. Transmission of the signals betweenthe sensor signal transmitter 9 and the sensor signal receiver 13 andtransmission of the electric power between the electric powertransmitter 12 and the electric power receiver 8 are carried outwireless by means of, for example, electromagnetic waves.

It is to be noted that the sensors 6C to 6E may be utilized either todetect the same parameters, for example, the temperatures or to detectdifferent parameters, for example, the number of revolutions, thetemperature and the vibration.

It is also to be noted that one of the wireless sensor units 4A and 4Bemployed in the first embodiment of the present invention shown in FIG.1 may be of a design including the plural sensors 6C to 6E shown in FIG.8. In such case, the use is preferred of the signal coordinator 60.

A conceptual application of the wireless sensor system according to thefourth embodiment of FIG. 8 to the wheel support bearing assembly isshown in FIG. 9. In this application, the plural sensors 6C to 6E areused to detect the number of revolutions, the temperature and thevibration, respectively. The receiver-transmitter subunit 7, thetemperature sensor 6D and the vibration sensor 6E are mounted on theouter member 1 of the wheel support bearing assembly. The rotationsensor 6C is mounted on the outer member 1 so that the number ofrevolutions of the inner member 2 can be detected. The sensor signalreceiving unit 5 is disposed inside a tire house (not shown).

According to the conceptual application of FIG. 9, the mounting of thesingle wireless sensor unit 4 on the wheel support bearing assembly 33allows the detections of the number of revolutions, the temperature andthe vibrations simultaneously. Also, the electric power can be suppliedwireless to the wireless sensor unit 4 and, for this reason, a harness,which would otherwise extend between the tire house and the wheelsupport bearing assembly, can advantageously be dispensed with and,accordingly, not only can troubles such as breakage of the harnessresulting from collision of stones be avoided, but also the wirelesssensor unit 4 can be light-weighted. Also, the use of the plural sensors6C to 6D is effective to render the bearing assembly to be functionallyintelligent, thus upgrading the automobile control. In addition, basedon bearing information such as temperature, the bearing assembly can bediagnosed to determine if it has any trouble.

The details of the wheel support bearing assembly of FIG. 9 are shown inFIG. 10. The wheel support bearing assembly 33 shown therein is of afourth generation type and includes the inner member 2 made up of a hubaxle 2A and an outer race 15A of the constant velocity universal joint15. Raceways each for the respective row of the rolling elements 3 areformed on an outer peripheral surface of the hub axle 2A and an outerperipheral surface of the outer race 15A.

The single wireless sensor unit 4 is mounted on the outer member 1 ofthe wheel support bearing assembly 33. The sensors 6C to 6E of thewireless sensor unit 4 are disposed within a sealed space in the wheelsupport bearing assembly 33, which is shielded from the outside, whereasthe electric power receiver 8 and the sensor signal transmitter 9 aremounted externally on the outer race 1. More specifically, the wirelesssensor unit 4 forms an integral unit, in which a circuit box 81 and asensor mount 82 are integrated together, and the circuit box 81 ismounted on an outer peripheral surface of the outer member 1. The sensormount 82 is accommodated within an annular bearing space between theouter member 1 and the inner member 2, having been inserted through aradial hole formed in the outer member 1.

The electric power receiver 8 and the sensor signal transmitter 9 aredisposed within the circuit box 81, and the sensors 6C to 6E areprovided in the sensor mount 82. The rotation sensor 6C is made up ofthe magnetic sensor 18 and the magnetic encoder 17 disposed inface-to-face relation with the magnetic sensor 18, while the magneticsensor 18 is disposed in the sensor mount 82. The magnetic encoder 17 ismounted on an outer peripheral surface of the inner member 2. This wheelsupport bearing assembly 33 also includes sealing members 84 and 85 forsealing opposite open ends of the annular bearing space delimitedbetween the outer and inner members 1 and 2. The sensors 6C to 6E arepositioned within this sealed bearing space and between the rows of therolling elements 3.

As described above, since the sensors 6C to 6E are disposed within thesealed bearing space in the bearing assembly 33, the sensors 6C to 6Ecan be protected from external dusts, foreign matter, water and so onand, therefore, the reliability and durability of the sensors 6C and 6Ecan advantageously be increased. In particular, since the wheel supportbearing assembly 33 is placed under the severe environment where it issusceptible to foreign matter and/or salty muddy water on the roadway,disposition of the sensors 6C to 6E within the sealed bearing space iseffective to increase the reliability and durability thereof. Theelectric power receiver 8 and the sensor signal transmitter 9 arepreferably disposed outside the wheel support bearing assembly 33 interms of wireless transmission efficiency.

It is to be noted that although the wheel support bearing assembly 33 ofFIG. 10 is a fourth generation type, the wheel support bearing assemblyof any generation type, for example, the third generation type can beemployed such that the sensors 6C to 6E may be disposed within thesealed bearing space while the electric power receiving unit 8 and thesensor signal transmitter 9 are disposed outside the wheel supportbearing assembly. Also, the wireless sensor unit 4 may include eitheronly one sensor or a plurality of sensors, one or some of which aredisposed outside the bearing assembly. By way of example, the wirelesssensor unit 4 disposed in the wheel support bearing assembly 33 shown inFIG. 10 may be one of the wireless sensor units 4A and 4B of the firstembodiment.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings which are used only for the purpose ofillustration, those skilled in the art will readily conceive numerouschanges and modifications within the framework of obviousness upon thereading of the specification herein presented of the present invention.By way of example, although in describing any one of the foregoingembodiments the use has been made of the single sensor signal receivingunit 5, a plurality of sensor signal receiving units can be employed inthe practice of the present invention. Where the plural sensor signalreceiving units are employed, those sensor signal receiving units may beused to receive the sensor signals transmitted from the sensor signaltransmitter of the same wireless sensor unit or to receive the sensorsignals transmitted from the sensor signal transmitter of the differentwireless sensor units.

Also, the sensor signal receiver and the electric power transmitter maynot be included within the same sensor signal receiving unit 5 and maybe disposed separated from each other. In addition, receipt of thesensor signals may be carried out by different sensor signal receivingunits and an electric power may be supplied wireless from the sameelectric power transmitter 12 to the plural wireless sensor units.

In addition, although in describing any one of the foregoing embodimentsthe wireless transmission has been described as carried out by theelectromagnetic waves, any transmitting method, for example, anelectromagnetic coupling, rays of light or ultrasonic waves can beemployed for transmitting the sensor signal and the electric operatingpower.

Accordingly, such changes and modifications are, unless they depart fromthe scope of the present invention as delivered from the claims annexedhereto, to be construed as included therein.

1. A wireless sensor system which comprises: a plurality of sensors fordetecting respective parameters to be detected; a sensor signaltransmitter for transmitting wireless sensor signals outputtedrespectively from the sensors; an electric power receiver for receivingwireless an electric operating power required to drive the sensors andthe sensor signal transmitter; a sensor signal receiver for receivingthe sensor signals transmitted from the sensor signal transmitter; andan electric power transmitter for transmitting the electric operatingpower wireless to the electric power receiver.
 2. The wireless sensorsystem as claimed in claim 1, wherein the sensor signal receiver has acapability of receiving the sensor signals from the respective sensors,which are transmitted by the sensor signal transmitter, and the electricpower transmitter is disposed in a sensor signal receiving unitincluding the sensor signal receiver.
 3. The wireless sensor system asclaimed in claim 1, further comprising a plurality of wireless sensorunits each including the sensors, the sensor signal transmitter and theelectric power receiver.
 4. The wireless sensor system as claimed inclaim 1, further comprising a single wireless sensor unit including thesensor, the sensor signal transmitter and the electric power receiver,wherein the plural sensors are provided in this single wireless sensorunit and wherein the sensor signal transmitter is operable to transmitwireless the sensor signals outputted from the plural sensors.
 5. Thewireless sensor system as claimed in claim 3, wherein some or all of theplural wireless sensor units each include the plural sensors and whereinthe respective sensor signal transmitters in such some or all of thewireless sensor units are operable to transmit wireless the sensorsignals outputted from the sensors.
 6. The wireless sensor system asclaimed in claim 3, wherein the plural wireless sensor units are mountedon different bearings in a machine plant.
 7. The wireless sensor systemas claimed in claim 3, wherein at least one of the plural wirelesssensor units includes the sensor utilized as a tire pressure sensor foran automotive vehicle or a rotation sensor for a wheel support bearingassembly.
 8. A wireless sensor system which comprises: a plurality ofwireless sensor units, each of the wireless sensor units including anelectric power receiver having a tuning circuit and a detecting andrectifying circuit for securing an electric operating power from anelectromagnetic wave of a predetermined power feeding frequency; asensor for detecting a parameter to be detected; and a sensor signaltransmitter for transmitting a signal outputted from the sensor as awireless sensor signal in the form of an electromagnetic wave of anatural frequency different from the power feeding frequency; and asensor signal receiving unit for supplying wireless the electricoperating power to each of those wireless sensor units and for receivinga sensor signal transmitted from each of those wireless sensor units,the sensor signal receiving unit including an electric power transmitterfor transmitting wireless the electromagnetic wave of the predeterminedpower feeding frequency and a sensor signal receiver for receiving thewireless sensor signal of the natural frequency that is transmittedwireless from each of the wireless sensor units.
 9. The wireless sensorsystem as claimed in claim 8, wherein the sensor signal receiver of thesensor signal receiving unit includes a plurality of receiving circuitseach operable to receive a signal of a single frequency corresponding tothe assigned natural frequency of the wireless sensor signal transmittedfrom each of the wireless sensor units.
 10. The wireless sensor systemas claimed in claim 8, wherein the sensor signal receiver of the sensorsignal receiving unit includes a plurality of tuning circuits eachoperable to receive a signal of a single frequency corresponding to theassigned natural frequency of the wireless sensor signal transmittedfrom each of the wireless sensor units, and a switching detector forswitching among outputs of the tuning circuits to select the outputs oneat a time on a time sharing basis and for detecting each of the selectedoutputs.
 11. The wireless sensor system as claimed in claim 8, whereinthe sensor signal receiver of the sensor signal receiving unit iscapable of varying a receiving frequency in correspondence with thenatural frequencies of the wireless sensor signals being transmittedthereto and is capable of receiving the wireless sensor signals byswitching among the receiving frequencies to select the receivingfrequencies one at a time on a time sharing basis.
 12. The wirelesssensor system as claimed in claim 8, wherein the electromagnetic wavefor power feeding has a plane of polarization that is different fromthat of the electromagnetic wave of the wireless sensor signal.
 13. Thewireless sensor system as claimed in claim 8, wherein the respectiveelectromagnetic waves of the wireless sensor signals transmitted fromthe associated wireless sensor units have different planes ofpolarization.
 14. The wireless sensor system as claimed in claim 8,wherein the plural wireless sensor units are mounted on differentbearings in a machine plant.
 15. The wireless sensor system as claimedin claim 8, wherein at least one of the plural wireless sensor unitsincludes the sensor utilized as a tire pressure sensor for an automotivevehicle or a rotation sensor for a wheel support bearing assembly.
 16. Abearing assembly equipped with a wireless sensor unit, which comprises:a plurality of wireless sensor units mounted on a bearing, each of thewireless sensor units including: a sensor for detecting a parameter tobe detected; a sensor signal transmitter for transmitting wireless asensor signal outputted from the sensor; and an electric power receiverfor receiving wireless an electric operating power required to drive thesensor and the sensor signal transmitter.
 17. A bearing assemblyequipped with a wireless sensor unit, which comprises: one of aplurality of wireless sensor units that is mounted on a bearing; theplural wireless sensor units each including a sensor for detecting aparameter to be detected; a sensor signal transmitter for transmittingwireless a sensor signal outputted from the sensor; and an electricpower receiver for receiving wireless an electric operating powerrequired to drive the sensor and the sensor signal transmitter; and theplural wireless sensor units being operable to transmit to a commonsensor signal receiver the respective sensor signals transmitted fromthe corresponding sensor signal transmitters and being also operable toreceive wireless the electric operating power from a common electricpower transmitter through the respective electric power receiver.
 18. Abearing assembly equipped with a wireless sensor, which comprises; aplurality of sensors for detecting respective parameters to be detected;a sensor signal transmitter for transmitting wireless sensor signalsoutputted from the respective sensors; and an electric power receiverfor receiving wireless an electric operating power required to drive thesensors and the sensor signal transmitter.
 19. The bearing assembly asclaimed in claim 16, wherein at least one of the sensors mounted on thebearing is a rotation sensor including a multipolar magnet, having aplurality of magnetic poles deployed in a direction circumferentiallythereof, and a magnetic sensor for detecting the magnetic poles of themultipolar magnet.
 20. The bearing assembly as claimed in claim 17,wherein at least one of the sensors mounted on the bearing is a rotationsensor including a multipolar magnet, having a plurality of magneticpoles deployed in a direction circumferentially thereof, and a magneticsensor for detecting the magnetic poles of the multipolar magnet. 21.The bearing assembly as claimed in claim 18, wherein at least one of thesensors mounted on the bearing is a rotation sensor including amultipolar magnet, having a plurality of magnetic poles deployed in adirection circumferentially thereof, and a magnetic sensor for detectingthe magnetic poles of the multipolar magnet.
 22. The bearing assembly asclaimed in claim 19, wherein the magnetic sensor is a magnetoresistivesensor.
 23. The bearing assembly as claimed in claim 20, wherein themagnetic sensor is a magnetoresistive sensor.
 24. The bearing assemblyas claimed in claim 21, wherein the magnetic sensor is amagnetoresistive sensor.
 25. The bearing assembly as claimed in claim16, wherein the sensor is disposed within a sealed space in the bearing,which is shielded from the outside, and the electric power receiver andthe sensor signal transmitter are disposed outside the bearing.
 26. Thebearing assembly as claimed in claim 17, wherein the sensor is disposedwithin a sealed space in the bearing, which is shielded from theoutside, and the electric power receiver and the sensor signaltransmitter are disposed outside the bearing.
 27. The bearing assemblyas claimed in claim 18, wherein the sensor is disposed within a sealedspace in the bearing, which is shielded from the outside, and theelectric power receiver and the sensor signal transmitter are disposedoutside the bearing.
 28. A wheel support bearing assembly for rotatablysupporting a vehicle wheel relative to a vehicle body structure, thewheel support bearing assembly comprising: an outer member having aplurality of outer raceways; an inner member having inner racewaysaligned with the outer raceways; a plurality of rows of rolling elementsinterposed between the outer raceways and the inner raceways; one of aplurality of wireless sensor units that is mounted on the wheel supportbearing assembly; the plural wireless sensor units each including asensor for detecting a parameter to be detected; a sensor signaltransmitter for transmitting wireless a sensor signal outputted from thesensor; and an electric power receiver for receiving wireless anelectric operating power required to drive the sensor and the sensorsignal transmitter; the plural wireless sensor units being operable totransmit the respective sensor signals to a common sensor signalreceiver through the corresponding sensor signal transmitters and isalso operable to receive wireless the electric operating power from acommon electric power transmitter through the electric power receiver.29. A wheel support bearing assembly for rotatably supporting a vehiclewheel relative to a vehicle body structure, the wheel support bearingassembly comprising: an outer member having a plurality of outerraceways; an inner member having inner raceways aligned with the outerraceways; a plurality of rows of rolling elements interposed between theouter raceways and the inner raceways; a plurality of sensors fordetecting respective parameters to be detected; a sensor signaltransmitter for transmitting wireless sensor signals outputted from therespective sensors; and an electric power receiver for receivingwireless an electric operating power required to drive the sensors andthe sensor signal transmitter.
 30. A wireless sensor system whichcomprises: a wheel support bearing assembly as defined in claim 28; asensor signal receiver for receiving the sensor signal transmitted fromthe sensor signal transmitter in the wheel support bearing assembly; andan electric power transmitter for transmitting wireless the electricoperating power to the electric power receiver; wherein the sensorsignal receiver and the electric power transmitter are disposed in atire house of the vehicle body structure, where the wheel supportbearing assembly is installed, or disposed in a portion of the vehiclebody structure, which is more distant from the tire house with respectto the wheel support bearing assembly.
 31. A wireless sensor systemwhich comprises: a wheel support bearing assembly as defined in claim29; a sensor signal receiver for receiving the sensor signal transmittedfrom the sensor signal transmitter in the wheel support bearingassembly; and an electric power transmitter for transmitting wirelessthe electric operating power to the electric power receiver; wherein thesensor signal receiver and the electric power transmitter are disposedin a tire house of the vehicle body structure, where the wheel supportbearing assembly is installed, or disposed in a portion of the vehiclebody structure, which is more distant from the tire house with respectto the wheel support bearing assembly.